The major objective of our research is to investigate the etiology of osteoporosis. A number of specific situations lead to the development of osteoporosis in an individual who may otherwise not be a candidate for this disease. Two of these are malabsorption of calcium and vitamin D and long-term treatment for epilepsy. The purpose of the additional bone biopsy evaluation presented in this supplement, is to delineate the precise morphological parameters seen in these two conditions and to relate the changes to the biochemical parameters measured. Bibliographic references: Jowsey, J.: Bone histology and hyperparathyroidism. Clinics endocrin. & Met. 3:267-284, 1974. Jowsey, J., Riggs, B.L. and Kelly, P.J.: Long-term experience with fluoride and fluoride combination treatment of osteoporosis. In, Calcium Metabolism, Bone and Metabolic Bone Diseases, 1973. Proceedings of the 10th Symposium on Calcified Tissues, Hamburg, Germany, pp. 151- 154. Edited by F. Kuhlencordt & H. P. Kruse, Springer-Verlag, Berlin, Heidelberg, New York, 1975.